1. Field of the Invention
This invention relates to a pneumatic tire, and more particularly to a pneumatic radial tire for passenger cars, particularly front-wheel-drive passenger cars having excellent steering stability and ride comfort and a low noise property by largely reducing noise level based on tire cavity resonant sound.
2. Description of Related Art
In the pneumatic tire for passenger car (pneumatic radial tire), the steering stability becomes particularly important. In order to render this performance into a highly excellent level, it is common to apply a hard or super-hard bead filler rubber to a bead portion.
On the other hand, the application of such a bead filler rubber lowers the ride comfort and raises a noise level due to the tire cavity resonant sound. In order to render the steering stability, ride comfort and noise property of the tire into higher levels together, therefore, it is proposed to variously change height, material, shape and the like of the bead filler rubber in the tire.
If it is intended to improve the ride comfort, there is adopted a simple means for reducing the height of the bead filler rubber. In this case, however, the longitudinal rigidity in the radial direction of the tire lowers, while the circumferential and lateral rigidities of the tire simultaneously lower. Since these three rigidities are simultaneously decreased, the steering stability and the noise property based on the tire cavity resonant sound are simultaneously degraded. In other words, it is difficult to simultaneously establish the steering stability, ride comfort and noise property at higher levels.
It is, therefore, an object of the invention to provide a pneumatic tire having the steering stability, ride comfort and noise property at considerably higher levels.
According to the invention, there is the provision of a pneumatic tire comprising a tread portion, a pair of sidewall portions, a pair of bead portions, a carcass of one or more rubberized plies containing radially arranged cords therein and extending between a pair of bead cores embedded in the respective bead portion to reinforce these portions, a belt reinforcing the tread portion and a bead filler rubber taperingly extending between a main body and a turnup portion of the carcass outward from the bead core in a radial direction of the tire, wherein said bead filler rubber in an assembly of the tire and an approved rim has a height lower than a height of a rim flange, and the turnup portion of the carcass has a height corresponding to not less than 0.5 times a section height SHc of the carcass from a rim size line RL and extends over a maximum width position of the carcass and in parallel to the main body of the carcass outward from a taper end of the bead filler rubber, and a pair of sidewall reinforcing layers are arranged along an outside of the turnup portion so as to extend from a position near to the taper end of the bead filler rubber up to at least a position near to an end of the belt.
In this case, the term xe2x80x9capproved rimxe2x80x9d used herein means a rim described every the kind and size of the tire in JATMA YEAR BOOK 1999.
In a preferable embodiment of the invention, the bead filler rubber has a JIS A-hardness within a range of 50-150 and an inner edge of the bead filler rubber in the radial direction of the tire has a width corresponding to 1.0-1.5 times a maximum width of the bead core in a rotating axial direction of the tire.
In another preferable embodiment of the invention, the sidewall reinforcing layer has a thickness of 0.3-5.0 mm and a tensile modulus of 0.5-500 kgf/cm2 in the circumferential direction of the tire.
In the other preferable embodiment of the invention, the sidewall reinforcing layer is made from a rubber composition having a tensile modulus of 0.5-50 kgf/cm2.
In a further preferable embodiment of the invention, the sidewall reinforcing layer is made from a rubberized cord layer having a tensile modulus of 0.5-500 kgf/cm2, and the rubberized cord layer contains organic fiber cords arranged at an inclination cord angle of not less than 0xc2x0 with respect to a circumferential direction of the tire.